1. Field of the Invention
The present invention relates to a polymer, and a resist composition, in particular, a chemically amplified positive resist composition that exhibit high resolution, good in-plane dimension uniformity of developed resist patterns on substrates such as mask blanks and excellent etching resistance, and that are suitable as micro patterning compositions, in particular, for fabricating VLSIs or photomasks.
2. Description of the Related Art
In recent years, a finer pattern rule is demanded as high integration and high-speed of LSIs have been realized. Under the circumstances, deep-ultraviolet lithography is considered promising as a next generation microprocessing technique. The deep-ultraviolet lithography allows for processing equal to or less than 0.5 μm. Use of a resist composition having a low optical absorbance in the deep-ultraviolet lithography allows for patterns with wall profiles almost vertical to substrates.
A chemically amplified positive resist composition (For example, see Japanese Examined Patent Application Publication No. 02-27660; and Japanese Unexamined Patent Application Publication No. 63-27829) using an acid as a catalyst has been developed in recent years. The chemically amplified positive resist composition exhibits high sensitivity, high resolution, and high dry etching resistance by using a high-intensity KrF excimer laser as a deep ultra-violet light source. Therefore, the chemically amplified positive resist composition is expected as a promising resist composition for deep-ultraviolet lithography having excellent features.
As for such a chemically amplified positive resist composition, there are known a two-component system composed of a base polymer and an acid generator; and a three-component system composed of a base polymer, an acid generator, and a dissolution inhibitor having an acid labile group.
For example, Japanese Unexamined Patent Application Publication No. 62-115440 suggests a resist composition composed of poly-p-tert-butoxystyrene and an acid generator. Similar to this suggestion, Japanese Unexamined Patent Application Publication No. 03-223858 suggests a two-component system resist composition composed of a resin having a tert-butoxy group intramolecularly and an acid generator. Furthermore, Japanese Unexamined Patent Application Publication No. 04-211258 suggests a two-component system resist composition composed of polyhydroxystyrene having a methyl group, an isopropyl group, a tert-butyl group, a tetrahydropyranyl group, or a trimethylsilyl group and an acid generator.
In addition, Japanese Unexamined Patent Application Publication No. 06-100488 suggests a resist composition composed of a polyhydroxystyrene derivative such as poly[3,4-bis(2-tetrahydropyranyloxy)styrene], poly[3,4-bis(tert-butoxycarbonyloxy)styrenel], or poly[3,5-bis(2tetrahydropyranyloxy)styrene] and an acid generator.
However, when a base resin has a tert-butyl group as an acid labile group, the resist composition has a high baking optimum temperature of about 130° C. When a base resin has a tert-butoxycarbonyl group as an acid labile group, the resist composition exhibits low resolution. In both cases, the resist compositions tend to provide T-top pattern profiles. On the other hand, an alkoxyalkyl group such as an ethoxyethyl group or a 2-tetrahydropyranyl group is decomposed by a weak acid. Therefore, a resist composition with a base resin having an alkoxyalkyl group as an acid labile group has a drawback in which the pattern profile thins considerably as time passes from exposure to a heat treatment. Furthermore, such a resist composition is not compatible with use of a resist film with thinner thickness resulting from reductions in size. In addition, the resist composition lacks heat resistance and causes contamination of the lens of an exposure system by outgassing from resist upon development. Therefore, at present, every resist composition has problems and not compatible with reductions in size.
There is reported another resist composition containing a copolymer of hydroxystyrene and a tertiary (meth)acrylate for the purpose of realizing higher transparency and higher adhesion to a substrate, ameliorating footing profile to a substrate, and enhancing etching resistance (see Japanese Unexamined Patent Application Publications No. 03-275149 and No. 06-289608. However, such a resist composition has problems of insufficient heat resistance, providing poor pattern profiles after development, and the like. Therefore, the resist composition is not satisfactory. In addition, the resist composition provides poor in-plane dimension uniformity of developed resist patterns on substrates such as mask blanks, which becomes more of a problem as pattern line width is reduced in size.
At present, as higher resolution is achieved, thinner patterns are used concurrently. Under the circumstances, there is a demand for a resist composition that exhibits good in-plane dimension uniformity of developed resist patterns on substrates such as mask blanks and high etching resistance.